Study of the formation of the photosynthetic apparatus (chromatophore) of Athiorhodaceae will be undertaken as a model for cellular differentiation: A. Regulation and transmission of genetic information for chromatophore formation by plasmid genes will be investigated by: (1) analyzing and isolating plasmid DNA's from various Athiorhodaceae by analytical and preparative ultracentrifugation and DNA-DNA hybridization; (2) studying the spontaneous and induced loss of genetic information for chromatophore formation; (3) determining if genetic information for photosynthesis can be transmitted, intra- or interspecifically, and (4) determining if mRNA specific to the photosynthetic state is homologous to plasmid DNA's by RNA-DNA hybridization. B. The genetic system of Rps. capsulata is being used to construct a map of the photosynthesis region of the genome. C. The mechanism of O2 repression of the chromatophore will be studied by isolation and analysis of mutants with an altered response to O2. D. The regulatory mechanism which controls chromatophore formation will be examined by analysis of mutants with conditional regulatory defects.